1. Field of the Invention
The present invention relates to the field of coating processes, particularly those processes used to coat optical materials.
2. Art Background
Typically, during the manufacture of an optical material a coating is applied to one or more surfaces of the material to achieve the desired optical characteristics of tint, increased abrasion resistance, anti-reflection properties, or to provide some other desired optical quality. For example, optical lenses are typically coated with a silicone anti-abrasion coating such as Dow Corning Q9-6312 or General Electric Coating SHC 1200, which may form part of an optical article such as for example eyeglasses, goggles, visors and the like.
Lenses coated according to one method used in the prior art are immersed into a coating solution and then removed for drying. Another method commonly used is to spin the lens and to flow a coating material at an angle onto the surface of the optical element. However, in the case where multi-focal lens elements are to be coated (such as bi or tri focals), coating methods known in the prior art do not provide aberration free optical surfaces since the coating material tends to flow along the top ledge of the multi-focal element and puddle or streak prior to drying (see FIG. 1). In addition, where a spray or immersion coating method is used to coat a multi-focal optical lens, frequently a fillet of dried coating material forms at the top ledge separating the primary optical surface from the secondary generally semi-circular optical region (see FIG. 2). If a tint or dye is then applied to the multi-focal lens, the fillet takes on a darker appearance by absorbing more of the tint or dye, and a dark segment line is visible. This line optically and cosmetically interferes with the use of the lens and is therefore undesirable.
The inability of standard coating processes to achieve a distortion-free coating frequently renders the lens element unusable, inasmuch as the puddles and/or drip lines contribute to eyestrain and a degradation of image quality for the user. Accordingly, there exists a need for a coating process which provides a uniform, aberration-free coating, on multi-focal lenses and other optical articles having discontinuities on the optical surface.
As will be discussed below, the present invention overcomes the disadvantages of the prior art coating methods, and provides a uniform distortion free coating an optical materials, particularly multi-focal lenses.